Body portions of structures, such as trains, automobiles, ships, and so forth, have hitherto been reinforced by combining a plurality of structural members. For example, the floor of an automotive body (hereinafter simply referred to as “floor”) has rigidity not only for primarily resisting the torsion and bending of the vehicle body when the vehicle is driven, but also for transferring an impact load in case of collision of the vehicle. The floor also affects the weight of the automotive body significantly. Thus, the floor is required to have mutually contradicting properties, that is, a high rigidity and a light weight. The floor includes flat panels that are joined to each other by welding, vehicle widthwise members that have a substantially gutter-shaped cross section and are fixed to the flat panels along the vehicle widthwise direction, and vehicle longitudinal members that have a substantially gutter-shaped cross section and are fixed to the flat panels along the front-back direction of the vehicle body.
The flat panels include, for example, dash panels, front floor panels, and rear floor panels. The vehicle widthwise members are structural members that are disposed along the vehicle widthwise direction of these flat panels and fixed thereto by welding, etc., so as to increase the rigidity and strength of the floor. The vehicle widthwise members include, for example, floor cross members, and seat cross members. The vehicle longitudinal members are structural members that are disposed along the front-back direction of a vehicle body and fixed thereto by welding, etc., so as to increase the rigidity and strength of the floor. The vehicle longitudinal members include, for example, side sills, side members, and the like.
Among them, the structural members, such as the vehicle widthwise members and the vehicle longitudinal members, are typically joined to other members via outward flanges formed at the ends of the structural members. For example, a floor cross member, which is an example of the vehicle widthwise members, is joined to other members, such as a tunnel portion of a front floor panel and a side sill, via outward flanges that are formed at both ends of the floor cross member.
FIGS. 27 and 28 illustrate a floor cross member 1, which is a representative example of a member joined to other members with outward flanges 4 formed at both ends in the longitudinal direction of the member. FIG. 27 is a perspective view of the floor cross member 1 and FIG. 28 is a view on an arrow A in FIG. 27.
A front floor panel 2 is reinforced, for example, by a tunnel portion (not shown) that is joined to the upper surface (indoor-side surface) of the front floor panel 2, and also by a side sill 3 and the floor cross member 1. The tunnel portion is a structural member projecting toward the inside of a vehicle along the substantially widthwise center of the front floor panel 2. The side sill 3 is spot welded to the upper surface of the front floor panel 2 at each widthwise edge of the front floor panel 2. Both ends of the floor cross member 1 are spot welded to the tunnel portion and the side sill 3 via the outward flanges 4 formed at both ends in the longitudinal direction of the floor cross member 1. This improves the rigidity and the load transfer properties of the floor when an impact load is applied.
For example, Patent Literatures 1 and 2 each disclose a structural member for an automotive body that is disposed along the vehicle widthwise direction of an automobile and has a substantially gutter-shaped cross section including a gutter bottom, ridges, and vertical walls. The structural member described in Patent Literature 1 has such a shape that the height of the vertical walls becomes gradually larger toward an end of the structural member so as to match the shape of another member that is joined to the structural member at its opening end having a gutter-shape cross section. The structural member described in Patent Literature 2 has such a shape that the width of the gutter bottom becomes gradually larger toward an end of the structural member.